ABSTRACT The vocal folds are exposed to ~25 million pollutant, viral, and bacterial insults each day and require protection from this myriad of inhaled insults. Mucus is the thin layer of fluid that covers the surface of the vocal folds and is the first line of defense in the larynx. However, an increased amount of thick, tacky mucus is commonly observed on the vocal folds in persons with inflammatory voice disorders. This phenomenon, described as ?mucus aggregation,? is not trivial. Mucus aggregation is one of the most common complaints of persons with voice disorders and leads to phonotraumatic behaviors, negatively impacts vocal fold vibration and voice quality, and may even promote the accumulation of noxious irritants in the larynx. Currently, a major obstacle in treating mucus aggregation is that biological mechanisms regulation laryngeal mucus production in normal or inflamed larynges are not known. The overarching objective of this proposal is to elucidate cellular and molecular mechanisms underlying laryngeal mucus production and to assess clinical mucus aggregation and vocal function during normal and inflammatory conditions. The central hypothesis is that biological mechanisms implicated in mucus overproduction and clinical features of mucus aggregation will be appreciated in the inflammatory, but not normal condition. Cigarette smoke is a ubiquitous inhaled insult implicated in the development of voice disorders and known to induce chronic airway inflammation. Consequently, the first Specific Aim seeks to elucidate key biological and clinical properties of the laryngeal mucus layer in nonsmokers (normal condition) and smokers (inflammatory condition). In Part A, we will investigate cellular and molecular mechanisms implicated in mucus overproduction, including increased quantity and altered quality of mucus. In Part B, we will assess clinical mucus aggregation on the vocal folds and vocal function. The second Specific Aim will use a novel in vitro model system to measure the effect of cigarette smoke on inflammatory cytokine concentration and laryngeal mucus production. This proposal is innovative because it is the first to systematically elucidate biological mechanisms underlying the production of the laryngeal mucus layer. We expect to identify cellular and molecular changes consistent with mucus overproduction in an inflammatory, but not normal condition. This contribution, when integrated with concurrent clinical mucus aggregation findings from vocal function assessment, is expected to be significant, as it will provide insight into potential mechanisms underlying abnormal mucus aggregation on the vocal folds. These findings will add to the knowledge base necessary in order to develop strategies to normalize the laryngeal mucus layer. Such strategies will likely not only have a positive impact on voice production, but also overall laryngeal health.